Steering Angle Sensing Four-Wheel Steering System (4WS) / 1987

A Prophetic Concept Produces the World's First Four-Wheel Steering System

Can We Utilize the Rear Wheels of FF Cars?

The 1960s were a decade of dramatic progress in science and engineering. In space, NASA's Apollo missions fostered boundless dreams and aspirations, as man took his first glorious steps upon the surface of the moon. And on Earth, people were beginning to see visions of an ever-advancing automotive technology. It all meant the promise of a bright future.

The rapid popularization of automobiles in the 1960s backlashed in the 1970s, however. Various problems began to emerge, from environmental pollution and traffic congestion to growing numbers of traffic accidents and recalls of defective vehicles. In response to public concerns, significant efforts were made to address these problems. The ESV (Experimental Safety Vehicle) program, led by NHTSA (National Highway Traffic Safety Administration, a U.S. agency), was one such effort.

The ESV's objective was to conduct a fundamental review of automobile safety, with the intention of lowering the rising tide of traffic accidents. It was a matter of global consensus, with automobile manufacturers around the world joining the program. With its automobile operations finally getting on track, Honda decided to participate in the program as well, though on a semi-official level. As a result, research was begun on an experimental safety vehicle.

Automotive safety generally falls into two categories: "Collision avoidance" and "active safety." Honda's themes of research were explored from the perspective of enhanced active safety in the areas of maneuverability, stability and dynamic performance. In other words, the research aimed at developing responsive vehicles that could more easily avoid obstacles and, when necessary, come to a quick, complete stop. It was this research effort that ultimately laid the foundation for subsequent evolutionary developments in power steering. Another of the possibilities examined through Honda's research was a hydraulic suspension system designed to prevent centrifugal force from affecting the driver.

The assurance of active safety, which was the main target of the research, meant that Honda would have to identify fundamentally effective mechanisms in order to achieve better dynamic performance. At the end of 1977, Honda held a brainstorming session in the hope of returning to the basics through a review of fundamental vehicle structures. This brainstorming session gave birth to the concept of a 4-wheel steering (4WS) system.

Honda vehicles were at the time essentially front-engine, front-wheel-drive (FF) models. In an FF vehicle the rear wheels play a relatively minor role, since the front wheels perform around 80 percent of the steering, driving and braking. Compared to the front wheels, the rear wheels are merely in place as a means of support, ensuring that the car moves ahead in a straight and predictable fashion.

The brainstorming session produced certain discussions that led to an interesting fact: although there were cars with four-wheel brake systems and four-wheel drive, steering control was universally given to the front wheels. Naturally, they wondered if they could utilize the idle rear wheels to provide some steering function. With that, an initial concept was defined. The fact that only Honda had vehicles of FF specification made the idea all the more intriguing. If the rear wheels could be employed in a way that provided some steering control, dynamic performance would improve significantly. The research engineers began to ponder that question, and as they did their desire for a new challenge was awakened.